Electromagnetic control devices, also referred to as actors or actuators, control motors or displacement magnets, are widely known in control technology. For example, they serve to drive or actuate control valves or flap gates for controlling the through-flow of gaseous or liquid media. Most electromagnetic actuators are bistable, i.e. they have only two stable positions, for example ‘on’ or ‘off’.
From DE 103 10 448 A1 a bistable actuator is known, which comprises two coils and an armature formed as a permanent magnet arranged on an armature rod. The polarity of the permanent magnet is orientated along the displacement direction of the armature, and the permanent magnet is held by the coils either in one or the other of its end positions. The coil configuration in this case forms a two-pole system, whereby the permanent magnet is attracted by one coil and at the same time repelled by the other coil, and vice-versa. This shortens the switching time.
From DE 102 07 828 A1 a bistable electromagnetic displacement magnet is known, whose polarity is orientated radially, i.e. transversely to the movement direction of the armature.
Besides bistable actuators, tristable actuators are also known: from DE 1 892 313 U a displacement electromagnet with three stable positions, namely two outer end positions and a central position, is known. The displacement electromagnet comprises a total of four coils, two stationary permanent magnets, two outer housing-antipoles, two inner housing-antipoles and two armatures that can move longitudinally on a push-rod. In each case an end position is reached by energizing an outer coil, the armatures being attracted by the energized coil. In contrast, the central position of the push-rod is reached when the armatures are held by the permanent magnets, which are in contact on both sides against the inner housing-antipoles (partition wall). The disadvantage of this known displacement electromagnet are that it comprises a large number of parts, namely four coils, two permanent magnets and two armatures, which also make for substantial extra weight.